Projector and trapezoidal distortion correcting method

ABSTRACT

A projector includes: capturing section that images an object on which an image is projected to produce a captured image; a projection distance information generating section that generates projection distance information representing a projection distance, which is the distance to the object on which an image is projected; a judging section that judges based on the projection distance information whether the projection distance exceeds a reference value; and a correcting section that performs trapezoidal distortion correction based on boundary lines of the object on which an image is projected contained in the captured image when the projection distance exceeds the reference value, whereas performing trapezoidal distortion correction based on at least coordinate information representing three-dimensional coordinates of the object on which an image is projected when the projection distance does not exceed the reference value.

BACKGROUND

1. Technical Field

The present invention relates to a projector, an information storingmedium, and a trapezoidal distortion correcting method.

2. Related Art

As a trapezoidal distortion correcting method employed in a projector(trapezoidal distortion correction is also called, for example,trapezoidal correction and keystone correction), for example,JP-A-2005-229293 proposes a correcting method in which a plurality ofphase difference sensors is used to measure the distances to a pluralityof measurement points on an object on which an image is projected, andJP-A-2005-347790 proposes a correcting method in which an image sensoris used to capture an image and acquires information on the peripheralboundary lines of an object on which an image is projected.

In the distance measuring method, however, since the measurementprecision decreases when the distance to the object on which an image isprojected increases, the projector cannot correct a trapezoidaldistortion accurately. On the other hand, in the method carried out byacquiring information on the peripheral boundary lines or the shape ofthe object on which an image is projected, the projector cannot correcta trapezoidal distortion accurately because part of the captured imageincludes no boundary line when the distance to the object on which animage is projected decreases.

SUMMARY

An advantage of some aspects of the invention is to provide a projector,an information storing medium, and a trapezoidal distortion correctingmethod that allow a trapezoidal distortion to be corrected accuratelyirrespective of the projection distance.

A projector according to an aspect of the invention includes ancapturing section that captures an object on which an image is projectedto produce a captured image, a projection distance informationgenerating section that generates projection distance informationrepresenting a projection distance, which is the distance to the objecton which an image is projected, a judging section that judges based onthe projection distance information whether the projection distanceexceeds a reference value, and a correcting section that performstrapezoidal distortion correction based on boundary lines of the objecton which an image is projected contained in the captured image when theprojection distance exceeds the reference value, whereas performingtrapezoidal distortion correction based on at least coordinateinformation representing three-dimensional coordinates of the object onwhich an image is projected when the projection distance does not exceedthe reference value.

A trapezoidal distortion correcting method according to yet anotheraspect of the invention is used in a projector, and the method includesthe steps of capturing an object on which an image is projected by usinga capturing device to produce a captured image, generating projectiondistance information representing a projection distance, which is thedistance to the object on which an image is projected, judging based onthe projection distance information whether the projection distanceexceeds a reference value, and performing trapezoidal distortioncorrection based on boundary lines of the object on which an image isprojected contained in the captured image when the projection distanceexceeds the reference value, whereas performing trapezoidal distortioncorrection based on at least coordinate information representingthree-dimensional coordinates of the object on which an image isprojected when the projection distance does not exceed the referencevalue.

According to the aspects of the invention, the trapezoidal distortioncorrection can be performed by using the projection distance-basedmethod, whereby the trapezoidal distortion correction can be performedaccurately irrespective of the projection distance.

The projection distance information generating section may generate theprojection distance information based on the captured image.

In the thus configured projector, the projection distance informationcan be generated and the trapezoidal distortion correction can beperformed by using only the captured image without measuring theprojection distance with a distance sensor, prompting a user to selector input a value representing the projection distance, or any otheroperation.

The correcting section may include a boundary line informationgenerating section that generates based on the captured image boundaryline information on the coordinates of the boundary lines of the objecton which an image is projected contained in the captured image, and afirst distortion correction information generating section thatgenerates based on the boundary line information first distortioncorrection information for performing the trapezoidal distortioncorrection.

In the thus configured projector, the trapezoidal distortion correctioncan be performed in accordance with the shape or any other suitableparameter of the object on which an image is projected.

The correcting section may include a coordinate information generatingsection that generates based on the captured image coordinateinformation representing the three-dimensional coordinates of aplurality of points on the object on which an image is projected, aprojection angle information generating section that generatesprojection angle information representing the projection angle based onthe coordinate information, and a second distortion correctioninformation generating section that generates based on the projectionangle information second distortion correction information forperforming the trapezoidal distortion correction.

In the thus configured projector, the trapezoidal distortion correctioncan be performed in accordance with the projection angle.

The second distortion correction information generating section maygenerate the second distortion correction information based on theprojection angle information and the boundary line information.

In the thus configured projector, the trapezoidal distortion correctioncan be performed in accordance with the shape or any other suitableparameter of the object on which an image is projected and theprojection angle.

The correcting section may include a trapezoidal distortion correctingsection that performs trapezoidal distortion correction based on thefirst distortion correction information when the projection distanceexceeds the reference value, whereas performing trapezoidal distortioncorrection based on the second distortion correction information whenthe projection distance does not exceed the reference value.

In the thus configured projector, the trapezoidal distortion correctioncan be performed by selecting distortion correction information inaccordance with the projection distance.

The projection distance information generating section may generate theprojection distance information based on the coordinate information.

In the thus configured projector, the projection distance informationcan be generated in accordance with the three-dimensional coordinates ofthe plurality of points on the object on which an image is projected.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a functional block diagram of a projector in a firstembodiment.

FIG. 2 is a flowchart showing a trapezoidal distortion correctingprocedure in the first embodiment.

FIG. 3 diagrammatically shows vanishing points in the first embodiment.

FIG. 4 shows an exemplary measurement image in the first embodiment.

FIG. 5 diagrammatically shows vanishing points in a three-dimensionalspace in the first embodiment.

FIG. 6 diagrammatically shows an example of the vanishing points in thecoordinate system of an imaginary area in the first embodiment.

FIG. 7 diagrammatically shows another example of the vanishing points inthe coordinate system of the imaginary area in the first embodiment.

FIG. 8 is a functional block diagram of a projector in a secondembodiment.

FIG. 9 is a flowchart showing a trapezoidal distortion correctingprocedure in the second embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments in which the invention is applied to a projector will bedescribed below with reference to the drawings. It is noted that theembodiments described below do not limit in any sense the contents ofthe invention set forth in the claims. It is further noted that all theconfigurations shown in the following embodiments are not necessarilyessential for solutions in the invention set forth in the claims.

First Embodiment

A projector according to the present embodiment has a function ofgenerating two pieces of distortion correction information by using twotypes of method, selecting one of the two pieces of distortioncorrection information in accordance with the projection distance, andusing the selected distortion correction information to correct atrapezoidal distortion. A description will be made of function blocks ofa projector having the function described above.

FIG. 1 is a functional block diagram of a projector 100 in the firstembodiment. The projector 100 includes an capturing section 110 thatcaptures an image for measurement or other purposes to produce acaptured image, an image inputting section 120 to which imageinformation (RGB signals, for example) is inputted from a PC (PersonalComputer) or any other apparatus, a projection distance informationgenerating section 130 that generates projection distance informationrepresenting the projection distance, a judging section 140 that judges,for example, whether the projection distance exceeds a reference value,a correcting section 150 that performs trapezoidal distortion correctionand other operations, and a projecting section 190 that projects animage.

The correcting section 150 includes a boundary line informationgenerating section 152 that generates boundary line informationrepresenting the position of an outer frame of a screen and otherparameters thereof, a coordinate information generating section 154 thatgenerates coordinate information representing three-dimensionalcoordinates of a predetermined point on the screen, a projection angleinformation generating section 155 that generates projection angleinformation representing a projection angle, a first distortioncorrection information generating section 157 that generates firstdistortion correction information, a second distortion correctioninformation generating section 159 that generates second distortioncorrection information, and a trapezoidal distortion correcting section162 that performs trapezoidal distortion correction.

The projector 100 may use the following hardware to achieve thefunctions described above: For example, the projector 100 may use a CCDcamera or any other suitable device as the capturing section 110, animage signal input port, a converter, and other components as the imageinputting section 120, a CPU and other components as the projectiondistance information generating section 130 and the judging section 140,a CPU, an image processing circuit, and other components as thecorrecting section 150, and a lamp, a liquid crystal panel, a liquidcrystal drive circuit, a projection lens, and other components as theprojecting section 190.

A computer accommodated in the projector 100 may read a program storedin an information storing medium 200 and function as the projectiondistance information generating section 130 and other sections. Examplesof the information storing medium 200 may include a CD-ROM, a DVD-ROM, aROM, a RAM, and an HDD.

A description will next be made of a trapezoidal distortion correctingprocedure using the sections described above. FIG. 2 is a flowchartshowing the trapezoidal distortion correcting procedure in the firstembodiment.

The capturing section 110 captures an image of the screen, which is onetype of object on which an image is projected, with no image or a blackimage projected thereon to produce a first captured image (step S1). Theboundary line information generating section 152 generates boundary lineinformation on the coordinates of the boundary lines of the screen basedon the first captured image (step S2).

The screen may, for example, have a rectangular white area and a blackarea provided around the white area. In this case, the white area is anarea where a projected image can be displayed, and the boundary betweenthe white and black areas corresponds to the boundary lines. Thecoordinate information may be information representing the coordinatesof end points of each of the boundary lines, information representingthe coordinates of at least one point on each of the boundary lines andinclination thereof, or any other suitable information.

Based on the boundary line information, the first distortion correctioninformation generating section 157 sets a correction target area in animage formation area of a liquid crystal panel, the correction targetarea representing an area where an image having undergone trapezoidaldistortion correction is displayed, and generates first distortioncorrection information representing the coordinates of the four cornersof the correction target area in the image formation area (step S3).

More specifically, for example, when the boundary lines in the capturedimage form a rectangle, that is, when the captured image contains fourboundary lines, the first distortion correction information generatingsection 157 sets the correction target area by converting thecoordinates of the end points of each of the boundary lines in thecaptured image (capturing coordinate system) into the coordinates in aprojection coordinate system.

When the captured image contains at least one but fewer than or equal tothree boundary lines, the first distortion correction informationgenerating section 157 sets the correction target area by determininginfinite points for the boundary lines of the screen, for example, inthe projection coordinate system, the origin of which is the principalpoint of the projection lens, converting the coordinates of the infinitepoints into the coordinates of vanishing points in the projectioncoordinate system, and interpolating a straight line(s) passing throughthe vanishing points as a missing side(s) (missing boundary line(s)).

FIG. 3 diagrammatically shows the vanishing points in the firstembodiment. For example, in the example shown in FIG. 3, three sides(three boundary lines) of the screen, the upper side, the lower side,and the left side, have been detected. When three sides have beendetected, the first distortion correction information generating section157, based on a vanishing point in the vertical or horizontaldirections, determines a vanishing point in the other direction.

Specifically, in the example shown in FIG. 3, for example, the firstdistortion correction information generating section 157 sets in theplane corresponding to Z=1 an imaginary area 20 parallel to the imageformation area of the liquid crystal panel and having the same shape asthat of the image formation area in the three-dimensional projectioncoordinate system, the origin O of which is the principal point of theprojection lens, and computes the coordinates of a horizontal vanishingpoint Hp where an extension of the upper side of the screen intersectsan extension of the lower side thereof.

A vertical vanishing point Vp is on an extension of the left side, andthe vanishing points and the origin O form a right angle. The firstdistortion correction information generating section 157 uses the factdescribed above to compute the coordinates of the vertical vanishingpoint Vp where an extension of the left side of the screen 10 intersectsan extension of the right side thereof.

As described above, when both the upper and lower sides and the left orright side have been detected, the first distortion correctioninformation generating section 157 can set a correction target area bycomputing the coordinates of each of the vanishing points to interpolatea missing side.

When both the left and right sides and upper or lower side have beendetected, the first distortion correction information generating section157 can interpolate a missing side and hence set a correction targetarea by swapping the computation procedure described above between thevertical and horizontal directions and computing the coordinates of eachof the vanishing points. When all the four sides have been detected, thefirst distortion correction information generating section 157 can set acorrection target area by using the coordinates of the intersections ofthe sides.

While the description has been made of the case where at least threesides have been detected, the first distortion correction informationgenerating section 157 can set a correction target area when only one ortwo sides have been detected. For example, let θ and φ be the pitchangle and the yaw angle, respectively, representing the projectionangle, and assume that the roll angle is zero. In this case, thetwo-dimensional coordinates of the vertical vanishing point Vp isexpressed by Equation (1), and the two-dimensional coordinates of thehorizontal vanishing point Hp is expressed by Equation (2).

$\begin{matrix}{{Vp} = ( {0,\mspace{14mu}{- \frac{1}{\tan\;\theta}}} )} & (1) \\{{Hp} = ( {\frac{1}{\tan\;\phi \times \cos\;\theta},\mspace{14mu}{\tan\;\theta}} )} & (2)\end{matrix}$

For example, when only two sides, the upper and lower sides, have beendetected, the first distortion correction information generating section157 can determine the coordinates of the horizontal vanishing point Hpby computing the intersection of an extension of the upper side and anextension of the lower side. In this case, the first distortioncorrection information generating section 157 can determine the pitchangle θ by using the coordinates of the horizontal vanishing point Hpand the equation for computing the two-dimensional coordinates thereof(Equation 2), and substitute the pitch angle θ into the equation forcomputing the two-dimensional coordinates of the vertical vanishingpoint Vp (Equation 1) to determine the two-dimensional coordinates ofthe vertical vanishing point Vp.

Further, for example, when only two sides, the upper or lower side andthe left or right side, have been detected, the first distortioncorrection information generating section 157 can determine thetwo-dimensional coordinates of the vertical vanishing point Vp and thepitch angle θ by using the coordinates of one of the detected left andright sides and Equation 1. In this case, the first distortioncorrection information generating section 157 can also determine thetwo-dimensional coordinates of the horizontal vanishing point Hp byusing the coordinates of one of the detected upper and lower sides, thepitch angle θ, and Equation 2.

Moreover, for example, when only two sides, the left and right sides,have been detected, the first distortion correction informationgenerating section 157 can determine the two-dimensional coordinates ofthe vertical vanishing point Vp by computing the intersection of anextension of the left side and an extension of the right side. In thiscase, the two-dimensional coordinates of the horizontal vanishing pointHp is set to infinity (∞, 0).

As described above, the first distortion correction informationgenerating section 157 can set a correction target area by using thecoordinates of each of the detected sides and the coordinates of each ofthe vanishing points even when only two sides have been detected.

Further, for example, when only one side, the upper or lower side, hasbeen detected, the first distortion correction information generatingsection 157 sets the two-dimensional coordinates of the verticalvanishing point Vp to infinity (0, ∞), assumes the pitch angle θ to bezero, and then uses the coordinates of the detected side and Equation 2to determine the two-dimensional coordinates of the horizontal vanishingpoint Hp.

Further, for example, when only one side, the left or right side, hasbeen detected, the first distortion correction information generatingsection 157 uses the coordinates of the detected side and Equation 1 todetermine the two-dimensional coordinates of the vertical vanishingpoint Vp and sets the two-dimensional coordinates of the horizontalvanishing point Hp to infinity (∞, 0).

As described above, the first distortion correction informationgenerating section 157 can set a correction target area by using thecoordinates of each of the detected sides and the coordinates of each ofthe vanishing points even when the number of detected sides is one. Whenthe captured image contains no boundary line, the projector 100 mayproject a message image that prompts a user to check, for example, theposition where the projector 100 is installed.

The trapezoidal distortion correcting section 162 produces on the liquidcrystal panel a measurement image for measuring a plurality of referencepoints, and the projecting section 190 projects the measurement image onthe screen 10. The capturing section 110 captures the measurement imageprojected on the screen 10 to produce a second captured image (step S4).

FIG. 4 shows an exemplary measurement image 300 in the first embodiment.The measurement image 300 includes a patterned image formed of fourrectangles arranged in two rows by two columns connected to one another.That is, the patterned image is formed by drawing three straight linesparallel to the vertical direction and evenly spaced apart and threestraight lines parallel to the horizontal direction and evenly spacedapart in such a way that they intersect at right angles and 9intersections (reference points) in total are generated. The spacebetween the straight lines may be 200 pixels or greater when the liquidcrystal panel has, for example, 1024×768 pixels. In the projector 100,when the straight lines, which form the pattern, are spaced apart fromeach other, measured brightness or any other parameter of one line willnot interfere with that of the adjacent line.

Each of the straight lines contained in the patterned image hasgradation so that a central portion of the line is the brightest portionand a peripheral portion of the line is the darkest portion. Forexample, the measurement image 300 shown in FIG. 4 has a white area inthe central portion of each of the lines, light gray areas that sandwichthe white area, and dark gray areas that sandwich the light gray areas.

The width of each of the areas may be, for example, 4 pixels or greater.The background around the patterned image is an area having a grayscale(white or black area, for example) different from that of the peripheralarea (the dark gray area in the present embodiment) of the patternedimage. When the background around the patterned image has a grayscaledarker (black, for example) than that of the peripheral area of thepatterned image, the measurement image 300 has four different grayscalesin the entire image including the patterned image and the backgroundtherearound. The measurement image 300 may alternatively have threedifferent grayscales in the entire image including the patterned imageand the background therearound, that is, may be an image including apatterned image formed of a white area and a light gray area and abackground image formed of a dark gray area. In other words, themeasurement image 300 may be an image including a first area having afirst grayscale (white area), a second area having a second grayscaledarker than the first grayscale (dark gray area), and a third areahaving a third grayscale darker than the first grayscale but brighterthan the second grayscale and provided between the first and secondareas (light gray area).

The coordinate information generating section 154 generates coordinateinformation representing the three-dimensional coordinates of theplurality of reference points based on the second captured image (stepS5). More specifically, the coordinate information generating section154 determines the coordinates of the 9 reference points contained inthe captured image, by performing parabolic approximation, gravitycenter computation, or any other suitable computation based on theinformation, for example, on brightness of the captured image. Thedetermined coordinates are two-dimensional coordinates in an area wherethe capturing section 110 forms an image (capturing coordinate system).

The coordinate information generating section 154 processes thetwo-dimensional coordinates by performing active stereoscopy-basedcomputation, which uses the parallax between the projection lens of theprojecting section 190 and an capturing lens of the capturing section110, to determine the three-dimensional coordinates of the referencepoints on the screen and produce coordinate information representing thethree-dimensional coordinates of the reference points. The thus producedthree-dimensional coordinates belong to the projection coordinatesystem, the origin of which is the principal point of the projectionlens.

The projection distance information generating section 130 generatesprojection distance information representing the projection distance,which is the distance from the projector 100 to the screen 10, based onthe coordinate information (step S6).

FIG. 5 diagrammatically shows vanishing points in the three-dimensionalspace in the first embodiment. For example, there is an infinite pointHi on an extension of a boundary line of the upper side in the screen 10(the solid line in the screen 10 shown in FIG. 5), as shown in FIG. 5.Further, there is an infinite point Vi on extensions of the left andright sides. The infinite point Vi is also on an extension of a straightline perpendicular to the upper side.

In practice, although the infinite points are infinitely away, they arediagrammatically shown in the interest of clarity of description of FIG.5. Although the infinite point Hi on the right side and the infinitepoint Vi on the upper side are used to determine the vanishing points inthe present embodiment, an infinite point on the left side and aninfinite point on the lower side may be used to determine the vanishingpoints. The positions of the vanishing points are invariant irrespectiveof which of the methods is employed. Further, although the liquidcrystal panel is located, in practice, in front of the principal point Oof the projection lens (in the −Z direction), it is assumed for thepurposes of simplicity of the description that the imaginary area 20having the same shape as that of the image formation area of the liquidcrystal panel is disposed, for example, at Z=1 in parallel to the XYplane.

For example, in FIG. 5, the projection distance is the distance DP fromthe principal point O of the projection lens to a predetermined point onthe screen 10 (the central reference point in the measurement image 300projected on the screen 10, for example).

The projection angle information generating section 155 uses at leastthree sets of three-dimensional coordinates among the three-dimensionalcoordinates of the 9 reference points described above to generateprojection angle information representing the vertical and horizontalinclination (projection angle) of the projection light relative to thescreen 10 (step S7).

The second distortion correction information generating section 159generates second distortion correction information representing acorrection target area on the liquid crystal panel based on theprojection angle information and the boundary line information (stepS8). More specifically, for example, when the captured image containsone to three boundary lines, the second distortion correctioninformation generating section 159 generates second distortioncorrection information representing the correction target area by usingthe boundary line information and the projection angle information todetermine vanishing points and interpolating a line segment(s) on thestraight line(s) passing through the vanishing points as the missingboundary line(s).

More specifically, the second distortion correction informationgenerating section 159 can determine the vertical vanishing point Vp andthe horizontal vanishing point Hp in the coordinate system (projectioncoordinate system) of the imaginary area 20 by projecting the infinitepoints shown in FIG. 5 on the plane of the imaginary area 20.

FIG. 6 diagrammatically shows an example of the vanishing points in thecoordinate system of the imaginary area 20 in the first embodiment. FIG.7 diagrammatically shows another example of the vanishing points in thecoordinate system of the imaginary area 20 in the first embodiment.

For example, as shown in FIG. 6, when only one boundary line has beendetected, the second distortion correction information generatingsection 159 makes up the missing sides by using the projection angleinformation, the coordinates of the boundary line, and the coordinatesof the vanishing points to set straight lines passing through thevanishing points, followed by determining the coordinates of the fourcorners of a target area ABCD in the imaginary area 20 so that apredetermined condition is satisfied. A correction target area on theliquid crystal panel is thus set.

The target area ABCD is an area corresponding to the correction targetarea on the liquid crystal panel. The predetermined condition describedabove, for example, corresponds to a condition in which a correctedimage satisfies a predetermined aspect ratio (4:3 or 16:9, for example),a condition in which the largest possible area of the liquid crystalpanel is used, or any other suitable condition.

For example, as shown in FIG. 7, when two or more boundary lines havebeen detected, the second distortion correction information generatingsection 159 makes up the missing side(s) by using the projection angleinformation, the coordinates of each of the boundary lines, and thecoordinates of the vanishing points to set a straight line(s) passingthrough the vanishing points, followed by determining the target areaABCD. A correction target area on the liquid crystal panel is thus set.

The judging section 140 judges whether the projection distance exceeds areference value based on the projection distance information (step S9).The reference value, for example, ranges from 3 to 5 meters, although itdepends on the capturing and other conditions.

When the projection distance exceeds the reference value, thetrapezoidal distortion correcting section 162 performs trapezoidaldistortion correction by setting a correction target area on the liquidcrystal panel based on the first distortion correction information andproducing an image in the correction target area (step S10).

On the other hand, when the projection distance does not exceed thereference value, the trapezoidal distortion correcting section 162performs trapezoidal distortion correction by setting a correctiontarget area on the liquid crystal panel based on the second distortioncorrection information and producing an image in the correction targetarea (step S11).

As described above, according to the present embodiment, the projector100 can perform trapezoidal distortion correction by using theprojection distance-based method, whereby the trapezoidal distortioncorrection can be performed accurately irrespective of the projectiondistance.

Further, according to the present embodiment, the projector 100 canperform trapezoidal distortion correction by using the projection angleinformation and the boundary line information even when the screen 10 isnot perpendicular to the ground but inclined thereto.

Further, according to the present embodiment, the projector 100 canproject an image having undergone trapezoidal distortion correction inan area along the boundary lines of the screen 10 by using theinformation on the boundary lines of the screen 10.

Further, according to the present embodiment, the projector 100 candetermine a correction target area by using only the two-dimensionalcoordinates of the imaginary area 20 without using any three-dimensionalcoordinates when the first distortion correction information isgenerated, and can determine a correction target area by usingthree-dimensional coordinates and the two-dimensional coordinates of theimaginary area 20 when the second distortion correction information isgenerated.

Second Embodiment

The distortion correction information generating method is not limitedto that described in the first embodiment, but a variety of variationscan be implemented. In a second embodiment, a distortion correctioninformation generating method different from that in the firstembodiment will be described.

FIG. 8 is a functional block diagram of a projector 101 in the secondembodiment. A correcting section 151 in the projector 101 differs fromthe correcting section 150 in the projector 100 in that a projectionangle information generating section 156 uses boundary line informationfrom a boundary line information generating section 153 to generateprojection angle information, a first distortion correction informationgenerating section 158 uses the projection angle information to generatefirst distortion correction information, and a second distortioncorrection information generating section 160 generates seconddistortion correction information without using the boundary lineinformation. The projector 101 may also read a program from aninformation storing medium 201 and function as the first distortioncorrection information generating section 158 and other sections.

A trapezoidal distortion correcting procedure in the projector 101 willnext be described. FIG. 9 is a flowchart showing the trapezoidaldistortion correcting procedure in the second embodiment. The steps S1and S2 are the same as those in the first embodiment.

The projection angle information generating section 156 generates firstprojection angle information representing the projection angle based onthe boundary line information from the boundary line informationgenerating section 153 (step S21). The first distortion correctioninformation generating section 158 generates first distortion correctioninformation based on the first projection angle information (step S22).

More specifically, for example, the first distortion correctioninformation generating section 158 may figure out the projection anglein the vertical direction and the projection angle in the horizontaldirection based on the first projection angle information and use, forexample, data that relate the projection angles to the coordinates of acorrection target area to generate first distortion correctioninformation representing the correction target area in accordance withthe projection angles.

The steps S4 to S6 are the same as those in the first embodiment. Theprojection angle information generating section 156 generates secondprojection angle information representing the projection angles based onthe coordinate information from the coordinate information generatingsection 154 (step S23). Since the first projection angle information isbased on the boundary lines of the screen 10, whereas the secondprojection angle information is based on the three-dimensionalcoordinates of the reference points in the measurement image 300 on thescreen 10, the first and second projection angle information may differfrom each other in some cases.

The second distortion correction information generating section 160generates second distortion correction information based on the secondprojection angle information, for example, by using the data describedabove (step S24). The steps S9 to S11 are the same as those in the firstembodiment.

As described above, the present embodiment also provides the sameadvantageous effect as that provided by the first embodiment.

Other Embodiments

The invention is not necessarily applied to the embodiments describedabove, but a variety of variations can be implemented. For example, inthe projectors 100 and 101 described in the above embodiments, theprojection distance is judged after two types of distortion correctioninformation are generated. The distortion correction information mayalternatively be generated after the judgment of the projection distanceand in accordance with the judgment result.

The reference value used to choose which of the trapezoidal distortioncorrecting methods may be determined in accordance with, for example,the size of the screen 10, which is an object on which an image isprojected. For example, the judging section 140 may determine thereference value based on information representing user's selection ofthe type of the screen, data representing the size of the screen, orother information and make the judgment by using the thus determinedreference value.

The object on which an image is projected is not limited to the screen10, but may be a blackboard, a whiteboard, a wall, a column, a desk, orany other suitable object.

The measurement image 300 is not limited to that described in the aboveembodiments. For example, the patterned image in the measurement image300 may have straight lines that lie off the contour of the patternedimage shown in FIG. 4 (for example, a #-like shape when the patternedimage is rectangular).

The number of grayscales of the patterned image described above isthree, but the number may be four or greater. Further, areas having thesame grayscale are disposed on both sides of the white area in thepatterned image described above, but areas having different grayscalesmay alternatively be disposed only on one side. For example, thepatterned image may be a linear image formed of a leftmost dark grayarea, a central light gray area, and a rightmost white area.

The coordinate information produced by the coordinate informationgenerating section 154 is not limited to the information representingthree-dimensional coordinates in the projection coordinate system, butmay, for example, be information representing three-dimensionalcoordinates in the capturing coordinate system. That is, when theprojection lens and the capturing lens are located substantially in thesame position in the projector 100 or 101, two-dimensional coordinatesin the capturing coordinate system may be directly converted intothree-dimensional coordinates in the capturing coordinate system.

Further, each of the projectors 100 and 101 generates the coordinateinformation on the boundary lines of the screen by capturing the screenwith no image projected thereon. Alternatively, when the boundary linesof the screen can be detected from the measurement image, the coordinateinformation on the boundary lines of the screen may be generated basedon the captured measurement image.

The projection distance information generating section 130 mayalternatively generate the projection distance information in accordancewith a measured value from a distance sensor, an adjustment value usedto drive a focus adjustment lens at the time of projection, user'sselection of the projection distance when an image that prompts the userto select the projection distance is projected, user's input of a valuerepresenting the projection distance, or any other suitable parameter.

Each of the projectors 100 and 101 is not limited to a (transmissive orreflective, such as LCOS) liquid crystal projector, but may, forexample, be a projector using a DMD (Digital Micromirror Device). DMD isa trade name of Texas Instruments Incorporated, USA. The functions ofthe projector 100 or 101 may be distributed to a plurality of apparatus(for example, a PC and a projector, an external camera and a projector,and other combinations).

The entire disclosure of Japanese Patent Application No. 2009-140119,filed Jun. 11, 2009 is expressly incorporated by reference herein.

1. A projector comprising: a capturing section that captures an objecton which an image is projected to produce a captured image; a projectiondistance information generating section that generates projectiondistance information representing a projection distance, which is thedistance to the object on which an image is projected; a judging sectionthat judges based on the projection distance information whether theprojection distance exceeds a reference value; and a correcting sectionthat performs trapezoidal distortion correction based on boundary linesof the object on which an image is projected contained in the capturedimage when the projection distance exceeds the reference value, whereasperforming trapezoidal distortion correction based on at leastcoordinate information representing three-dimensional coordinates of theobject on which an image is projected when the projection distance doesnot exceed the reference value.
 2. The projector according to claim 1,wherein the projection distance information generating section generatesthe projection distance information based on the captured image.
 3. Theprojector according to claim 1, wherein the correcting section includesa boundary line information generating section that generates based onthe captured image boundary line information on the coordinates of theboundary lines of the object on which an image is projected contained inthe captured image, and a first distortion correction informationgenerating section that generates based on the boundary line informationfirst distortion correction information for performing the trapezoidaldistortion correction.
 4. The projector according to claim 1, whereinthe correcting section includes a coordinate information generatingsection that generates based on the captured image the coordinateinformation representing the three-dimensional coordinates of aplurality of points on the object on which an image is projected, aprojection angle information generating section that generatesprojection angle information representing the projection angle based onthe coordinate information, and a second distortion correctioninformation generating section that generates based on the projectionangle information second distortion correction information forperforming the trapezoidal distortion correction.
 5. The projectoraccording to claim 4, wherein the second distortion correctioninformation generating section generates the second distortioncorrection information based on the projection angle information and theboundary line information.
 6. The projector according to claim 4,wherein the projection distance information generating section generatesthe projection distance information based on the coordinate information.7. A projector comprising: a capturing section that captures an objecton which an image is projected to produce a captured image; a projectiondistance information generating section that generates projectiondistance information representing a projection distance, which is thedistance to the object on which an image is projected; a judging sectionthat judges based on the projection distance information whether theprojection distance exceeds a reference value; and a correcting sectionthat performs trapezoidal distortion correction based on boundary linesof the object on which an image is projected contained in the capturedimage when the projection distance exceeds the reference value, whereasperforming trapezoidal distortion correction based on coordinateinformation representing three-dimensional coordinates of the object onwhich an image is projected and the boundary lines when the projectiondistance does not exceed the reference value.
 8. A trapezoidaldistortion correcting method comprising the step of: capturing an objecton which an image is projected by using a capturing device to produce acaptured image; generating projection distance information representinga projection distance, which is the distance to the object on which animage is projected; judging based on the projection distance informationwhether the projection distance exceeds a reference value; andperforming trapezoidal distortion correction based on boundary lines ofthe object on which an image is projected contained in the capturedimage when the projection distance exceeds the reference value, whereasperforming trapezoidal distortion correction based on at leastcoordinate information representing three-dimensional coordinates of theobject on which an image is projected when the projection distance doesnot exceed the reference value.